A liquid crystal display device used for a liquid crystal television, a liquid crystal display, etc. usually has a liquid crystal alignment film to control the liquid crystal alignment state provided therein. Heretofore, as the liquid crystal alignment film, a polyimide liquid crystal alignment film obtained by applying a liquid crystal aligning agent containing as the main component a solution of a polyimide precursor such as a polyamic acid (polyamide acid) or a soluble polyimide to a glass substrate or the like and baking it has been mainly used.
Along with a tendency to high precision of a liquid crystal display device, from demands for suppression of a decrease in the contrast of the liquid crystal display device and a reduction of a residual image, for a liquid crystal alignment film, not only development of an excellent liquid crystal alignment property and a stable pretilt angle is required, but also properties such as a high voltage retention, suppression of a residual image which occurs due to alternating-current drive, a low residual charge when a direct-current voltage is applied, and/or quick relaxation of the residual charge accumulated by a direct-current voltage, become more important.
For a polyimide liquid crystal alignment film, in order to meet the above demands, various proposals have been made. For example, as a liquid crystal alignment film with a short time until disappearance of a residual image which occurs due to a direct-current voltage, one obtained by using a liquid crystal aligning agent containing a polyamide acid and/or imide group-containing polyamide acid and in addition, containing a tertiary amine having a specific structure (Patent Document 1), one using a liquid crystal aligning agent containing a soluble polyimide using as a raw material a specific diamine compound having a pyridine skeleton or the like (Patent Document 2) etc. have been proposed. Further, as a liquid crystal alignment film with a high voltage retention and with a short time until disappearance of a residual image which occurs due to a direct-current voltage, one using a liquid crystal aligning agent containing a polyamide acid or an imidized polymer thereof and in addition, a very small amount of a compound selected from a compound containing one carboxylic acid group in its molecule, a compound containing one carboxylic acid anhydride group in its molecule and a compound having one tertiary amino group in its molecule, has been proposed (Patent Document 3).
Further, as a liquid crystal alignment film which is excellent in the liquid crystal alignment property, which has a high voltage retention, which produces little residual image, which is excellent in the reliability and which has a high pretilt angle, one using a liquid crystal aligning agent containing a polyamide acid or an imidized polymer thereof obtained from tetracarboxylic acid dianhydride having a specific structure, tetracarboxylic acid dianhydride containing cyclobutane and a specific diamine compound has been known (Patent Document 4). Further, as a method for suppressing a residual image which occurs due to an alternating-current drive in an in-plane switching liquid crystal display device, a method of using a specific liquid crystal alignment film which has a favorable liquid crystal alignment property and which has a significant interaction with liquid crystal molecules has been proposed (Patent Document 5).
On the other hand, as a polymer component constituting a polyimide liquid crystal aligning agent, a polyamic acid ester has been reported to be excellent in the liquid crystal alignment stability and reliability since when it is subjected to heat treatment to imidize it, it does not undergo a decrease of the molecular weight (Patent Document 6). Since a polyamic acid ester usually has problems such as a low electrical resistivity and a high residual charge when a direct-current voltage is applied, and accordingly a liquid crystal aligning agent comprising a polyamic acid ester and a polyamic acid excellent in the electrical properties blended has been reported (Patent Document 7).